Measurement of $J/psi$ polarization in $pp$ collisions at $sqrt{s}=7$ TeV

An angular analysis of the decay $J/psi rightarrow mu^{+} mu^{-}$ is performed to measure the polarization of prompt $J/psi$ mesons produced in $pp$ collisions at $sqrt{s}=7; mathrm{TeV}$. The dataset corresponds to an integrated luminosity of 0.37 fb$^{-1}$ collected with the LHCb detector. The measurement is presented as a function of transverse momentum, $p_mathrm{T}$, and rapidity, $y$, of the $J/psi$ meson, in the kinematic region $2 < p_mathrm{T} < 15; mathrm{GeV}/c$ and $2.0<y<4.5$.